Head or body coils are necessary in MRI apparatus. They are commonly used both for providing radio frequency (RF) excitation signals and thereafter receiving a spin-echo or free induction decay signal indicating a characteristic of the specimen being examined. Since the so-called pickup signal is of a very small magnitude, it is important to maximize the signal above the ambient noise level. It is also desirable that the specimen or human patient (which inevitably comes in various sizes and shapes, depending on the body portion being imaged) uniformly fill the coil structure in an optimal manner.
FIG. 5 illustrates a prior art coil of the saddle type where two separate coils provide a magnetic field vector B1 through the effective centers of the coils with the main magnetic field, Bo, lying along a centerline. The associated Velcro fastening thus shifts the field vector depending on the size of the body portion.